OBJECTIVE: Formation of new blood vessels plays a key role in tumor growth and metastasis and may be supported by bone marrow-derived endothelial progenitor cells (EPCs). Different studies have demonstrated that the engagement of EPCs is fundamental for the progression of avascular micrometastatic tumors to lethal macrometastatic ones. We have recently shown that store-operated Ca2+ entry (SOCE) controls cell proliferation in endothelial colony forming cells (ECFCs). SOCE is contributed by the Ca2+-permeable channel, Orai1, and the ER Ca2+-sensor, Stim1. The search for novel molecular targets to exploit in the fight against cancer prompted us to investigate the expression and role served by SOCE in ECFCs isolated from patients suffering from renal cellular carcinoma (RCC). METHODS: ECFCs were isolated from the peripheral blood of healthy donors or patients suffering from RCC as described elsewhere. Changes in [Ca2+]i were monitored loading the cells with Fura-2/AM (4 µM, 30 min) and with the aid of a CCD camera. RESULTS: SOCE was activated by exposing cells to the classic “Ca2+ add-back” protocol in presence of either cyclopiazonic acid (CPA), a selective inhibitor of the SarcoEndoplasmic Reticulum Ca2+-ATPase (SERCA), or the physiological agonist, ATP. In both cases we found that SOCE was significantly higher in RCC-ECFCs as compared to control cells, while the intracellular Ca2+ release was smaller. SOCE was selectively inhibited by BTP-2, as previously reported in control cells, whereas carboxyamidotriazole (CAI), an orally active anti-angiogenic drug which is in phase II clinical trials of metastatic RCC, was less specific and affected also Ca2+ release. The higher amplitude of SOCE was associated to the over-expression, at both mRNA and protein level, of Stim1 and Orai1 in RCC-ECFCs, while Stim2, Orai2 and Orai3 were not differently expressed in these cells. Finally, pre-incubation with BAPTA, an intracellular Ca2+ buffer, BTP-2, and CAI dramatically affected RCC-ECFC proliferation and tubulogenesis. CONCLUSIONS: These data indicate that SOCE is over-expressed in ECFCs isolated from patients suffering of RCC due to the selective up-regulation of Stim1 and Orai1. SOCE controls RCC-ECFC proliferation and tubulogenesis and might, therefore, be regarded as a novel molecular target to device alternative anti-cancer treatments.